mg/dL and mmol/L
Blood glucose is reported in two units. The United States and some other countries use milligrams per decilitre (mg/dL); the United Kingdom, Canada, Australia and much of Europe use millimoles per litre (mmol/L). Because one mole of glucose weighs about 180 grams, the conversion factor is 18:
mmol/L = mg/dL ÷ 18
mg/dL = mmol/L × 18
| mg/dL | mmol/L | What the number is used for |
|---|---|---|
| 54 | 3.0 | Clinically significant low blood sugar (level 2) |
| 70 | 3.9 | Low blood sugar threshold (level 1) |
| 100 | 5.6 | Upper limit of normal fasting glucose (ADA) |
| 126 | 7.0 | Fasting glucose diagnostic of diabetes |
| 140 | 7.8 | 2-hour glucose tolerance: prediabetes starts |
| 180 | 10.0 | Common upper target after meals for people with diabetes |
| 200 | 11.1 | 2-hour or random glucose diagnostic of diabetes |
Diagnostic ranges
The American Diabetes Association (ADA) uses these cut-offs for adults who are not pregnant. A single test is never enough for a diagnosis; an abnormal result is normally repeated or confirmed with a second, different test.
| Test | Normal | Prediabetes | Diabetes |
|---|---|---|---|
| Fasting plasma glucose | below 100 mg/dL (5.6) | 100–125 mg/dL (5.6–6.9) | 126 mg/dL (7.0) or higher |
| 2 hours after 75 g glucose (OGTT) | below 140 mg/dL (7.8) | 140–199 mg/dL (7.8–11.0) | 200 mg/dL (11.1) or higher |
| HbA1c | below 5.7% | 5.7–6.4% | 6.5% or higher |
| Random glucose | 200 mg/dL (11.1) or higher with classic symptoms (thirst, frequent urination, weight loss) indicates diabetes | ||
The World Health Organization uses the same diabetes thresholds but sets the start of impaired fasting glucose at 110 mg/dL (6.1 mmol/L) instead of 100. That is why a fasting reading of 105 mg/dL may be called "prediabetes" in one country and "normal" in another.
Worked examples
| Reading | Converted | Test | ADA range |
|---|---|---|---|
| 92 mg/dL | 5.1 mmol/L | Fasting | Normal |
| 105 mg/dL | 5.8 mmol/L | Fasting | Prediabetes range |
| 7.4 mmol/L | 133 mg/dL | Fasting | Diabetes range |
| 9.2 mmol/L | 166 mg/dL | 2-hour OGTT | Prediabetes range |
| 65 mg/dL | 3.6 mmol/L | Any | Low (below 70 mg/dL) |
HbA1c and average glucose
HbA1c measures the share of haemoglobin with glucose attached, which reflects the average blood sugar over roughly the past two to three months. The ADAG study turned it into an estimated average glucose (eAG):
eAG (mg/dL) = 28.7 × HbA1c − 46.7
| HbA1c | eAG mg/dL | eAG mmol/L |
|---|---|---|
| 5.0% | 97 | 5.4 |
| 5.7% | 117 | 6.5 |
| 6.5% | 140 | 7.8 |
| 7.0% | 154 | 8.6 |
| 8.0% | 183 | 10.2 |
| 9.0% | 212 | 11.8 |
Many adults with diabetes aim for an HbA1c below 7%, but targets are set individually; older adults or people at risk of low blood sugar may have higher targets.
Getting an accurate reading
- Fasting means 8 hours without food or caloric drinks; water is fine.
- Wash and dry your hands before a finger-prick test. Sugar on the skin from fruit or food can give a falsely high result.
- Home meters and sensors are less precise than a lab. They are allowed to differ from laboratory values by about 15%, so use a lab test for diagnosis.
- Illness, stress, steroids and poor sleep can raise glucose temporarily.
- Continuous glucose monitors measure fluid under the skin and lag behind finger-prick readings by several minutes, especially when glucose is changing quickly.
Low blood sugar
Below 70 mg/dL (3.9 mmol/L) is low blood sugar (hypoglycaemia). Typical symptoms are shaking, sweating, a fast heartbeat, hunger, irritability and confusion. People who use insulin or certain tablets are usually advised to take about 15 g of fast-acting carbohydrate, such as juice or glucose tablets, and re-check after 15 minutes. Below 54 mg/dL (3.0 mmol/L), or any low with confusion or inability to swallow, needs urgent help.
This calculator is for general information about a single reading. It is not a diagnosis. Diabetes is diagnosed by a health professional using laboratory tests, usually repeated. Pregnancy, children and people already treated for diabetes have different targets.
Everyday targets for people with diabetes
Diagnostic cut-offs are different from the day-to-day targets used once diabetes is diagnosed. For many non-pregnant adults, the American Diabetes Association suggests:
| Measure | Common target |
|---|---|
| Before meals | 80–130 mg/dL (4.4–7.2 mmol/L) |
| 1–2 hours after starting a meal | below 180 mg/dL (10.0 mmol/L) |
| HbA1c | below 7% |
| Continuous glucose monitor "time in range" (70–180 mg/dL) | more than 70% of the day |
These are starting points, not rules. Your own targets may be tighter or looser depending on age, other conditions, the medicines you take and your risk of low blood sugar, so agree them with your care team.
Frequently asked questions
How do I convert mg/dL to mmol/L?
Divide by 18. For example, 126 mg/dL ÷ 18 = 7.0 mmol/L. To go back, multiply mmol/L by 18.
What is a normal fasting blood sugar?
Below 100 mg/dL (5.6 mmol/L) under ADA criteria. The WHO uses below 110 mg/dL (6.1 mmol/L).
Is 140 mg/dL after eating normal?
Two hours after a meal, most people without diabetes are below 140 mg/dL (7.8 mmol/L). The formal test uses a standard 75 g glucose drink rather than a meal.
What HbA1c equals an average of 154 mg/dL?
About 7.0%, using the ADAG formula eAG = 28.7 × HbA1c − 46.7.
What blood sugar should someone with diabetes aim for before meals?
A common ADA target is 80–130 mg/dL (4.4–7.2 mmol/L), but individual targets vary.
Sources
- American Diabetes Association. Standards of Care in Diabetes—2025, Section 2: Diagnosis and Classification of Diabetes. Diabetes Care, 2025.
- Nathan DM et al. Translating the A1C assay into estimated average glucose values (ADAG study). Diabetes Care, 2008.
- World Health Organization / IDF. Definition and diagnosis of diabetes mellitus and intermediate hyperglycaemia, 2006.
- American Diabetes Association. Hypoglycemia (low blood glucose).
Last reviewed 7 October 2026. Results are estimates; see our disclaimer.